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Dave Smith Instruments Pro 2

Anything about hardware musical instruments.

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ghettosynth
KVRAF
 
4036 posts since 13 Oct, 2009

Postby ghettosynth; Wed Jun 25, 2014 11:10 am Re: Dave Smith Instruments Pro 2

JCJR wrote:Would like to hands on revisit a lot of the old poly synths. I would at the time judge an axe as to whether it would pay for itself in playing commercial music people were willing to pay me to play. If it couldn't make a certain set of sounds I needed, maybe I didn't pay close enough attention to the other sounds an axe might have been good at, if they were sounds I didn't expect typical customers to tolerate at the time.


This is really an important point. In the past, you interpreted the value of a synth in terms of what else was available at the time as well as the musical context. In the mid 80s, brash and bold sampler tones were all the rage, so a Jupiter 8 sounded like the kind of synth that grandma might like at the time.

You needed polyphony back then because well, everything that you played had to have that.

This isn't true today. We can afford to have synths that do just a few things well because they sit in the context of virtually unlimited polyphony with other instruments. Other instruments even do many of the things that we might have pushed that analog synth to do in the past.

My memorymoog was lots worse to hold tune than the prophet. It was maddening. I wore out the screw holes taking that thing apart so much.


Yeah, the memorymoog had character, but it wasn't engineered very well.

For whatever reason, didn't get knocked out by roland such as super jupiter either, though people can make real sweet tracks with em. Maybe my ears were too narrow minded.


The Super Jupiter was rack mounted. Did you mean the Jupiter 8, or 6, also very different synths?
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 11:14 am Re: Dave Smith Instruments Pro 2

Now you're way out on a limb :)

A digitally controlled oscillator is really a VCO where the control voltage comes from a CPU controlled DAC.

A DO or digital oscillator is really a CPU controlled timer with waveshaping.
Could be called a feed forward oscillator since it does not reset by feedback but by the timer.

A DAC that plays back a CPU calculated waveform perhaps should then be called a WF or WFO?

You're right about the term DCO being misused.
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Developer and proud owner of http://www.dspsynth.eu
ghettosynth
KVRAF
 
4036 posts since 13 Oct, 2009

Postby ghettosynth; Wed Jun 25, 2014 11:32 am Re: Dave Smith Instruments Pro 2

janostman wrote:Now you're way out on a limb :)


No, I'm not.

A digitally controlled oscillator is really a VCO where the control voltage comes from a CPU controlled DAC.


This is a technically correct definition that doesn't mean anything or have any value in this conversation because that isn't how the term is used in the industry. You could use this definition to claim that virtually all VCO based synths from the 80s forward were DCOs. They are not and nobody describes them that way except for internet pedants trying to win an argument that they're destined to lose.

This is also very distinct from any variant where the DAC is providing the output waveform. You made a claim that DCOs sound harsh, they do not, all of this pedantry does not correct your statement. A DCO, by your newfound definition, doesn't sound "harsh" either, it's still an analog integrator.

You're right about the term DCO being misused.


I'm right period, but it doesn't matter. The term DCO conveys features to a synth buying audience, as does VCO.

None of this dancing, however, yields a definition of a DCO that sounds harsh.
Last edited by ghettosynth on Wed Jun 25, 2014 11:38 am, edited 1 time in total.
JCJR
KVRian
 
953 posts since 17 Apr, 2005

Postby JCJR; Wed Jun 25, 2014 11:36 am Re: Dave Smith Instruments Pro 2

ghettosynth wrote:
For whatever reason, didn't get knocked out by roland such as super jupiter either, though people can make real sweet tracks with em. Maybe my ears were too narrow minded.


The Super Jupiter was rack mounted. Did you mean the Jupiter 8, or 6, also very different synths?

Thanks, got the name wrong. I didn't pay enough attention to the big rolands with colorful sliders and buttons, after playing em and deciding that the ballpark of memorymoog or chroma polaris tone was more to my taste.

Got the polaris almost by accident. Shortly after initial shipping, they blew em out so cheap I ordered one sight unseen, but the thing was real pleasant, though nothing is perfect. It also had a sound on the feminine side, but could make lots of sounds. A shame it failed. Wouldn't have ever sold that one.

Can't recall if it had dco or vco. Always thought it was vco, but never gave any tuning issues.

====

Janostman, the vco's, in poly synths, had voltage input and the polyphony was supported by a single DAC multiplexed into a zillion cheap sample and hold circuits, providing numerous "stable" voltages for the oscs, filters, vca's, eg's. Controlled by a very busy wimpy cpu.

The dco's typically eliminated those multiplexed sample and hold circuits, by allowing the busy little cpu to write into dco registers and latch in the value, so it didn't have to be constantly updated to keep it alive and on pitch.

But some dco's such as poly 61, were a little more "digital" than that, as best I recall.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 11:54 am Re: Dave Smith Instruments Pro 2

Even Braveheart was killed? ;)
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Developer and proud owner of http://www.dspsynth.eu
ghettosynth
KVRAF
 
4036 posts since 13 Oct, 2009

Postby ghettosynth; Wed Jun 25, 2014 11:56 am Re: Dave Smith Instruments Pro 2

JCJR wrote:
ghettosynth wrote:
For whatever reason, didn't get knocked out by roland such as super jupiter either, though people can make real sweet tracks with em. Maybe my ears were too narrow minded.


The Super Jupiter was rack mounted. Did you mean the Jupiter 8, or 6, also very different synths?

Thanks, got the name wrong. I didn't pay enough attention to the big rolands with colorful sliders and buttons, after playing em and deciding that the ballpark of memorymoog or chroma polaris tone was more to my taste.

Got the polaris almost by accident. Shortly after initial shipping, they blew em out so cheap I ordered one sight unseen, but the thing was real pleasant, though nothing is perfect. It also had a sound on the feminine side, but could make lots of sounds. A shame it failed. Wouldn't have ever sold that one.

Can't recall if it had dco or vco. Always thought it was vco, but never gave any tuning issues.


They were a VCO synth, CEM based.

Janostman, the vco's, in poly synths, had voltage input and the polyphony was supported by a single DAC multiplexed into a zillion cheap sample and hold circuits, providing numerous "stable" voltages for the oscs, filters, vca's, eg's. Controlled by a very busy wimpy cpu.

The dco's typically eliminated those multiplexed sample and hold circuits, by allowing the busy little cpu to write into dco registers and latch in the value, so it didn't have to be constantly updated to keep it alive and on pitch.


Yes, but it's more than that. Assuming that the S/H circuit was perfectly stable, you still have independent expo converters for each oscillator. That's the key point with a VCO vs a DCO, pitch and phase stability are a function of analog circuits. This is not true in a DCO and is why people think that DCOs sound sterile.

But some dco's such as poly 61, were a little more "digital" than that, as best I recall.


Poly 61s used bog standard 8253 timer chips much like Oberheim. The poly6 was interesting because it had analog VCOs, but only one per voice, and a shared expo converter. So, to the extent that the expo converter contributes to the character between voices, it doesn't do so in the Poly 6.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 12:15 pm Re: Dave Smith Instruments Pro 2

The 8253 timers reset the timer to the value when you write it to the reload registers.
Some other timers don't.

A phase accumulator definitely doesn't because it only changes the increment.

That can make some phase differences in the sound if the timers are free running.

That can explain why people think they sound different?
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Developer and proud owner of http://www.dspsynth.eu
JCJR
KVRian
 
953 posts since 17 Apr, 2005

Postby JCJR; Wed Jun 25, 2014 12:23 pm Re: Dave Smith Instruments Pro 2

Yes, but it's more than that. Assuming that the S/H circuit was perfectly stable, you still have independent expo converters for each oscillator. That's the key point with a VCO vs a DCO, pitch and phase stability are a function of analog circuits. This is not true in a DCO and is why people think that DCOs sound sterile.

Thanks, hadn't thought about it in those terms, but the yamaha cs voice cards were exponential voltage vco, so I suppose there was a shared exponential converter in those as well.

Another thing that made those yamaha vco so stable, the chips had electronic controlled heaters on em. Can't recall whether the heater was external or internal to each chip. But it seemed rather elegant-- If the chip always runs at a controlled temp higher than ambient, removes much of the temp dependent tuning problems. Plus exponential converters were difficult to completely temp compensate.

I never had much sound programming use for the hipass filter in the cs. They were funky yamaha specific filter chips, designed multi mode with lp, hp, and bp outputs. So I rewired the voice cards in mine to change the hipass filter to bandpass, and wired the bandpass filter in parallel with the lopass, rather than the factory hp to lp series wiring. Thataway I could pick out two different resonance peaks in a signal, one from the lp and one from the bp. That seemed more useful than a hipass on an already semi-wimpy sounding instrument.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 12:28 pm Re: Dave Smith Instruments Pro 2

That's because there isn't much use of a HPF in a subtractive synth?
And definitely not in my band-limited dsp version of the same.

Sure, there are people who find a use for every feature you put in?
___________________________________________________
Developer and proud owner of http://www.dspsynth.eu
ghettosynth
KVRAF
 
4036 posts since 13 Oct, 2009

Postby ghettosynth; Wed Jun 25, 2014 1:05 pm Re: Dave Smith Instruments Pro 2

janostman wrote:The 8253 timers reset the timer to the value when you write it to the reload registers.
Some other timers don't.

A phase accumulator definitely doesn't because it only changes the increment.

That can make some phase differences in the sound if the timers are free running.

That can explain why people think they sound different?


Most of the differences in how early DCO synths sound are probably attributable to how the master clock was implemented, or features other than the DCO itself. Oberheim went out of their way (on the M6, not the M1000) to make sure that the two oscillators of a voice did not share the same master oscillator and use a less stable varactor tuned Hartley oscillator for the master. This helps some, but they still have a sterile quality to them. The simplest implementation is to just use a crystal oscillator which, by comparison, are extremely stable. The main difference between the 8254 and 8253 is in supported speed. The 8254 does allow you to read the control registers whereas the 8253 is write only.

Newer DCOs are based on different chips completely, of course. This doesn't explain anything about the Poly61 with respect to other synths of the day, however. There is no significant difference between 8253 based synths and custom Roland LSI based synths, for example, in terms of how the DCO phase behaves.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 1:15 pm Re: Dave Smith Instruments Pro 2

I know for sure how the 8253 behaves after writing numerous PWM audio applications on an early PC before the SB, USB and firewire audio made an entrance on the platform.

I think its more or less how the program is written.

On the Juno-106 the timers are written anytime and that causes a sort of phase difference that can be audiable.

Strike a single key many times and you hear it.
___________________________________________________
Developer and proud owner of http://www.dspsynth.eu
JCJR
KVRian
 
953 posts since 17 Apr, 2005

Postby JCJR; Wed Jun 25, 2014 1:22 pm Re: Dave Smith Instruments Pro 2

janostman wrote:That's because there isn't much use of a HPF in a subtractive synth?
And definitely not in my band-limited dsp version of the same.

Sure, there are people who find a use for every feature you put in?


Many people liked having the hp filter in that model and it was a selling point. Good for programming many classes of thin sounds. I just never had much use for thin sounds on analog synths.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 1:33 pm Re: Dave Smith Instruments Pro 2

I could go to the bank and ask for 100 grand to build a synth.
That would only end me up like Dave.

or for the country I live in, make it blue?

Food on the table is what its all about.
___________________________________________________
Developer and proud owner of http://www.dspsynth.eu
ghettosynth
KVRAF
 
4036 posts since 13 Oct, 2009

Postby ghettosynth; Wed Jun 25, 2014 2:18 pm Re: Dave Smith Instruments Pro 2

janostman wrote:I know for sure how the 8253 behaves after writing numerous PWM audio applications on an early PC before the SB, USB and firewire audio made an entrance on the platform.

I think its more or less how the program is written.


How the program is written can have an effect on the sound, but parent was talking about the difference between the Poly61 and other contemporary DCO based synths of the day.

On the Juno-106 the timers are written anytime and that causes a sort of phase difference that can be audiable.

Strike a single key many times and you hear it.


Every time you strike a key it's going to rewrite the timers, so what? Every time you move the bender, the timers get rewritten. This is true for the Poly61 as well, it's true for every synth that uses an 8253 as a DCO. What is also true is that there are significant differences in how the master clocks were implemented and the effort is generally proportional to the cost. Now, don't you think that if it were just about rewriting software that some effort would be made to compete given that we have evidence that effort was made in clock circuits?

You said:

The 8253 timers reset the timer to the value when you write it to the reload registers.
Some other timers don't.


The Juno 106 that uses the same 8253 timers as the Poly 61? The Poly61 is a two DCO synth, why would you think that it's comparable to the Juno106? It is more similar in basic architecture to the Oberheim M6 or the MKS-30 and the reason that people thought that it sounded more digital is much more likely to be related to the differences in clock circuitry which can be easily seen in the schematic. All attempt to ensure that the two voices do not have the same phase, but the approaches are completely different. If you compare the M1000 to the Poly61 I doubt that you will hear significant differences in DCO character given that you limit the M1K to the same modulation capabilities of the Poly61. They are both very sterile sounding. Roland and Oberheim both tried to use separate varactor tuned LC oscillators, Korg did not.

Other areas of significant difference are in the waveshaping. Moreover, I suspect that folks really attribute any difference to user interface.
janostman
KVRist
 
90 posts since 21 Aug, 2009, from Sweden

Postby janostman; Wed Jun 25, 2014 2:27 pm Re: Dave Smith Instruments Pro 2

The user interface doesn't make any noise at all.
However our nonsense discussion does.

Why don't we leave it there?
Or do you want the last word?

You can have it.
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Developer and proud owner of http://www.dspsynth.eu
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